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Rho GTPases Control Polarity, Protrusion, and Adhesion during Cell Movement

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      Abstract

      Cell movement is essential during embryogenesis to establish tissue patterns and to drive morphogenetic pathways and in the adult for tissue repair and to direct cells to sites of infection. Animal cells move by crawling and the driving force is derived primarily from the coordinated assembly and disassembly of actin filaments. The small GTPases, Rho, Rac, and Cdc42, regulate the organization of actin filaments and we have analyzed their contributions to the movement of primary embryo fibroblasts in an in vitro wound healing assay. Rac is essential for the protrusion of lamellipodia and for forward movement. Cdc42 is required to maintain cell polarity, which includes the localization of lamellipodial activity to the leading edge and the reorientation of the Golgi apparatus in the direction of movement. Rho is required to maintain cell adhesion during movement, but stress fibers and focal adhesions are not required. Finally, Ras regulates focal adhesion and stress fiber turnover and this is essential for cell movement. We conclude that the signal transduction pathways controlled by the four small GTPases, Rho, Rac, Cdc42, and Ras, cooperate to promote cell movement.

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      Rho GTPases and the actin cytoskeleton.

      The actin cytoskeleton mediates a variety of essential biological functions in all eukaryotic cells. In addition to providing a structural framework around which cell shape and polarity are defined, its dynamic properties provide the driving force for cells to move and to divide. Understanding the biochemical mechanisms that control the organization of actin is thus a major goal of contemporary cell biology, with implications for health and disease. Members of the Rho family of small guanosine triphosphatases have emerged as key regulators of the actin cytoskeleton, and furthermore, through their interaction with multiple target proteins, they ensure coordinated control of other cellular activities such as gene transcription and adhesion.
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        Cell migration: a physically integrated molecular process.

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          Rho, rac, and cdc42 GTPases regulate the assembly of multimolecular focal complexes associated with actin stress fibers, lamellipodia, and filopodia.

          Rho and rac, two members of the ras-related superfamily of small GTPases, regulate the polymerization of actin to produce stress fibers and lamellipodia, respectively. We report here that cdc42, another member of the rho family, triggers the formation of a third type of actin-based structure found at the cell periphery, filopodia. In addition to stress fibers, rho controls the assembly of focal adhesion complexes. We now show that rac and cdc42 also stimulate the assembly of multimolecular focal complexes at the plasma membrane. These complexes, which are associated with lamellipodia and filopodia, contain vinculin, paxillin, and focal adhesion kinase, but are distinct from and formed independently of rho-induced focal adhesions. Activation of cdc42 in Swiss 3T3 cells leads to the sequential activation of rac and then rho, suggesting a molecular model for the coordinated control of cell motility by members of the rho family of GTPases.
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            Author and article information

            Affiliations
            MRC Laboratory for Molecular Cell Biology, CRC Oncogene and Signal Transduction Group and Department of Biochemistry, University College London, London WC1E 6BT, United Kingdom
            Author notes

            Address correspondence to Alan Hall, MRC Laboratory for Molecular Cell Biology, University College London, Gower Street, London WC1E 6BT, United Kingdom. Tel.: 44-171-380-7909. Fax: 44-171-380-7805. E-mail: Alan.Hall@ 123456ucl.ac.uk

            Journal
            J Cell Biol
            The Journal of Cell Biology
            The Rockefeller University Press
            0021-9525
            1540-8140
            22 March 1999
            : 144
            : 6
            : 1235-1244
            2150589
            10087266
            Categories
            Regular Articles

            Cell biology

            wound healing, focal adhesion, polarity, ras, rho gtpases

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